The present invention relates in general to antennas, and more specifically, to techniques and apparatus for stacking transmit and receive antennas formed on a substrate.
Engineers have recently been designing devices that enable interoperability of products within the home, office, and in factories using industrial automation. These devices can be monitored wirelessly via a network, and controlled based on an open global standard known as the IEEE 802.15.4 standard, which is promulgated by the IEEE (Institute of Electrical and Electronics Engineers). IEEE 802.15.4 specifies the physical communication layers for a low power, short range wireless communication link operating in the 2.4 GHz radio frequency band.
ZigBee is an additional standard-developed by the ZigBee Alliance association of companies, which defines logical network, security, and application software that operates using the 802.15.4 physical communication layer. ZigBee specifies high-level communication protocols that allow broad-based deployment of reliable wireless networks with low complexity and low costs, thereby facilitating the integration of various types of equipment from different vendors. ZigBee supports robust mesh networking technologies, where messages can choose a number of routes to get from one node to another, thereby increasing the reliability of the network. These types of networks typically are used for remote monitoring and control applications, and require very little power, which means that the network can run using inexpensive batteries.
ZigBee is designed to be simpler and less expensive than other wireless network devices, such as wireless personal area network (WPAN) devices (e.g., Bluetooth devices). One way to reduce the cost of such devices is to reduce the size and number of parts in the transceiver. At one level, the transceiver can be fabricated on a single small printed circuit board, where most of the transceiver components are contained in an integrated circuit. At another level, the transceiver can be a fully integrated single chip radio, including signal processing circuits, transmitter and receiver circuits, and an antenna, where all components of a transceiver are integrated into a single chip or integrated circuit. This idea is known as “system-on-a-chip” (SOC).
Whether on a printed circuit board, or in a single chip radio, or in some other embodiment, a small antenna system for transmitting and receiving signals can be an advantage. Smaller antenna systems can be less expensive to manufacture and easier to fit within the form factor of the products in which the transceiver is used.